Design of bolted shear connectors used in cold-formed steel-lightweight concrete (CFS-LWC) systems
Rohola Rahnavard, Hélder D. Craveiro, Rui Simões, Shahabeddin Torabian, Benjamin W. Schafer
Abstract
Bolted shear connectors are being increasingly used in demountable solutions, especially in innovative cold-formed steel (CFS)-concrete composite beams. The design of steel-concrete composite beams is closely related to the performance of the shear connectors that transfer shear forces between the steel beam and the concrete slab. However, while existing design codes provide formulas for predicting the shear resistance of welded shear studs, their applicability to bolted shear connectors remains uncertain, especially when dealing with thin-walled steel sections. Moreover, the available design procedures (especially in EN 1994–1–1) are specified for concrete with density more than 1750 kg/m 3 , imposing limitations for lightweight concrete (LWC), specific connector steel grades, and a limited ratio of connector diameter to steel beam flange thickness. Furthermore, the transferred shear force causes compression stresses in the CFS flange, and its effect has yet to be studied; this is, therefore, the subject of this study. This study first presents a numerical modeling approach for bolted shear connectors used in CFS-lightweight concrete systems and validates it against the available tests. Then, a parametric study is conducted to study the behavior of the bolted shear connector by varying the CFS thickness, CFS material properties, connector diameter, connector grade, and LWC strength. The numerical results were then compared with design shear resistance predictions following available design standards. Finally, formulations were proposed to predict the shear resistance of a bolted shear connector as a function of slippage between the CFS beam and concrete slab. The need for a new formulation arose from findings in this paper, which revealed that a high ratio of bolt diameter to beam flange thickness failed due to the curling of the CFS flange at the connection point. Consequently, a new equation was proposed to account for bearing forces combined with local bending of the CFS beam at the connection, as well as potential failure modes of the bolts and concrete.